(1) Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of efficiently forming high quality oxide shallow trench isolation in the fabrication of integrated circuits.
(2) Description of the Prior Art
Shallow trench isolation (STI) is gaining substantial interest in integrated circuit manufacturing. Most STI uses ozone-TEOS (tetraethoxysilane) for gap-filling, then resist etchback and chemical mechanical polishing (CMP) for planarization.
The conventional STI approach as in U.S. Pat. No. 5,229,316 to Lee et. al, uses CMP as the preferred planarized etching technique. This is followed by a wet etching process to remove the sacrificial layer of material. This leaves a pillar of trench filling material projecting upwardly relative to an upper substrate surface. The pillar of trench filling material must then be smoothed over so that the shoulders of the trench are rounded. Rounded shoulders are required for subsequent processes, e.g., poly gate etching.
Fazan and Mathes, "A Highly Manufacturable Trench Isolation Process of Deep Submicron DRAMS," IEDM Tech Digest 93-57, p. 3.6.1 to 3.6.4, describes how wet etching combined with the formation of oxide disposable spacers are used to avoid sharp corners at the trench edges. This technique is also described in U.S. Pat. No. 5,433,794 to Fazan et al.
Sharp corners at the trench edges are to be avoided because they can be responsible for various device leakage mechanisms such as the anomalous subthreshold current, the Gate Induced Drain Leakage at the 3-D intersection of the gate-to-drain overlap region and the trench corner and poly-stringers which can short together polysilicon layers.
Chang and Sze, in ULSI Technology, by The McGraw-Hill Company, Inc., copyright 1996, p.354 show various dry etch chemistries for silicon nitride (SiN) and silicon dioxide (SiO.sub.2).
U.S. Pat. No. 5,731,241 to Jang et al shows a self-aligned sacrificial oxide layer over the STI isolation layer and an etch back of the sacrificial oxide layer. Jang does not simultaneously etch the silicon nitride layer and the oxide layer.
U.S. Pat. No. 5,229,316 to Lee et al shows a method for wet-etching the pillar of trench filling material to round the corners of the trench. The method etches the pillar of trench filling material separately from the nitride layer.
This invention uses a specialized dry etching recipe to replace the aforementioned two steps: (1) removal of the layer of sacrificial material and (2) smoothing of the pillar of trench filling material, with a single step that removes the layer of sacrificial material and leaves a rounded shoulder over the edges of the trench.